Measurement of the photorespiratory activity of the submerged aquatic plantMyriophyllum spicatumL.

Abstract

AbstractThe CO2compensation concentrations (points) of leaves of the submerged vascular aquatic plantMyriophyllum spicatumL. were determined in a closed aqueous system at pH 7.0 by a gas chromatographic technique and over the range 10–30deg;C were found to range from 36 to 46 cm3m−3in medium equilibrated with 21% O2(0.03 kgm−3), and 25 to 35 cm3m−3in medium equilibrated with 2% O2(0.03 kgm−3). The rates of true (TPS) and apparent (APS) photosynthesis of leaves were measured in medium equilibrated with 21% O2and buffered at pH 7.0, at subsaturating concentrations (12.8–18.8 mmol m−3) of dissolved inorganic carbor. (DIC) containing H14CO3, by determining the initial rates of uptake by the leaves of DIC and14C‐activity from the medium. The rate of photorespiration, the difference between TPS and APS, was 7.0–13.3% of TPS over the range of 10–25°C and rose to 29% of TPS at 35°C. The magnitude of the compensation point of this plant is therefore similar to, but is much less O2‐sensitive than, those of C3plants, and the photorespiratory rate, at DIC concentrations near the CO2compensation point, is very low compared to that of C3plants.